Electrical musical instrument



June 4, 1940. 2,203,432

T. J. GEORGE ELECTRICAL MUSICAL INSTRUMENT Filed Nov. 30, 1939 El $4 342F 34%. ll. 2a

ET- 35 35\F i 44 AMPLIFIER [rare/2 zor 05. J George Patented June 4,1940 UNITED STATES PATENT OFFICE ELECTRICAL MUSICAL INSTRUMENTApplication November 30, 1939, Serial No. 306,830

2 Claims.

My invention relates generally to electrical musical instruments, andmore particularly to improvements in instruments of this type, whereby agroup of generators, comprising a master 5 generator and a plurality ofcontrolled generators, may be utilized to supply frequencies for aplurality of notes greater than the number of generators employed.

A further object is to provide an improved frequency generating systemfor electrical musical instruments in which generators of a group ofharmonically related notes may be tuned simultaneously to generatefrequencies of a different group of harmonically related notes.

A further object is to provide an improved electrical musical instrumentin which the number of frequency generators required is a fraction ofthe number usually required.

Other objects will appear from the following description, referencebeing had to the accompanying drawing, in which:

Figure l is a wiring diagram showing representative portions of thecomplete instrument;

Figure 2 is a diagrammatic front elevational view oi a modified form ofkey switch arrangement; and,

Figure 3 is a vertical sectional view taken on the line 33 of Fig. 2.

In general, the instrument comprises a plurality of master oscillatorsgenerating the frequencies or" notes of the highest octave of theinstrument. Instead of having twelve such oscillators, a lesser numbermay be utilizes, the instrument disclosed being provided with six suchmaster oscillators.

Each master oscillator stabilizes the frequencies of a series ofcontrolled or slave oscillators which generate frequencies of the notesof the lower octaves, corresponding to the note of the highest octave towhich the master oscillator is tuned.

Since, in musical selections, it is very infrequent that adjacentsemi-tone notes are simultaneously played, a considerable saving iseffect- 0 ed in the present instrument by providing means for shiftingthe frequency of the master oscillator and its controlled oscillatorsthrough a semi-tone interval, controlling such semi-tone frequency shiftby depression of the keys.

For example, one of the master oscillators may be tuned to the frequencyof the note A5, being the A in the highest octave of the instrument, andoscillating at a frequency of 1760 c. p. s. When the note .AB is to besounded, the tuning of the oscillator is not disturbed, but when, forexample, a note suchas A511 is to be sounded, the depression of the A53key will tune the master oscillator to a frequency of the note A51;(1864.66 0. p. 5.) prior to the completion of the circuit through whicha signal from the master oscillator is derived. In a similar manner,depres-- sion of any of the other At keys of the instrument willcomplete a parallel circuit tuning the A master oscillator to the Atfrequency. The controlled oscillators will, of course, be shiftedproportionately, and will generate the frequency of At in theirrespective octaves.

Referring to Fig. 1, the instrument illustrated comprises a masteroscillator Ill and two controlled oscillators H and t2, the masteroscillator Ill being representative of the six master oscillatorsemployed, while the oscillators ii and I2 are representative of anysuitable number of controlled oscillators (depending upon the gamut ofthe instrument) the frequencies of which are stabilized by the masteroscillators;

A power supply It has a conductor l6 connected to its positive terminalfor supplying the plate and screen voltages for the oscillators. Themaster oscillator it may he of any suitable construction, but isillustrated herein as of the re-. laxation type, comprising a tetrode 08having a cathode 28, control grid 22, screen grid 24, and plate 26. Thecoupling between the input and output circuits is provided by anoscillation transformer Ti, 9. tap of which is connected to the cathode2t. Condensers Cl and C2 are connected between the end terminals of thetransformer TI and the tap thereof, these condensers being provided toimprove the frequency stability of the oscillator. A timing and blockingcondenser C3 is connected between one end terminal of the transformer TIand the grid 22.

The operating potential is supplied to the screen 24 through a voltagedropping resistance RI, which is connected between the conductor l6 andscreen 24, a by-pass condenser on being connected between the screen andground. The plate 26 is connected to the conductor It through a loadresistor R2, the signal being derived from the plate 26 through ablocking condenser 05 which is connected to ground through apotentiometer resistance R3.

The frequency of oscillation of the master oscillator I0 is controlledby a variable grid biasing resistor R4 which is connected to groundthrough a second variable resistor R5, or may be connected to groundthrough a conductor 28 as will appear hereinafter.

The master oscillator ll operates in the manner of a triode relaxationoscillator, the screen 24 functioning as the plate in a triodeoscillator, the current through the plate 25 being thus ineffective tochange the frequency of'osciliation. The frequency of oscillation isregulated by the adjustment of the resistance R4 in one instance, andthe resistances R4 and R5 under other conditions of operation. Therelative values of the resistance Rd (or resistances R4 and R5) andcondenser C3ai-e themaior factors determining the frequency ofoscillation. The resistance R! is first adjusted to a value such thatwhen the conductor 23 is grounded, the frequency of oscillation will-bethat of the note A53. Then, after disconnecting the conductor 28 fromground, the combined resistance of R8 and R5 is varied by adjustment ofresistance R5 to lower the oscillation frequency to that of the note A5.the oscillator l3 furnishes the frequency for either the note A53 or A5,depending upon whether or not theconductor 28 is connected to ground.

Each of the controlled oscillators ll, :12, etc., comprises a triode 38having its cathode connected to ground, its plate connected to conductor l5 through a load resistance R6, an oscillation transformer T2,one terminal of which is connected to the grid of the tube 30 through atiming condenser C5, the grid bias being controlled by an adjustabletiming and biasing reslstance R1 connected between the grid and cathode.The plate circuit includes a blocking condenser Cl connected between theplate and one of the terminals of the oscillation transformer T2. Thecathode is connected to the tap on the transformer winding T2. Thesignal is derived from the oscillator through apotentiometer resistanceR8, which shunts the plate winding of transformer T2. The resistance R3of the master oscillator and the resistance R3 serve as, means foradjusting the amplitude of the output signal, for voicing purposes.

The frequency of oscillation of the oscillator II is stabilized by asignal derived from the signal output of the oscillator 53 through acoupling condenser CB, which is connected to one end of the platewinding of transformer T2 associated with the oscillator H. Theoscillator H is tuned by means of its adjustable resistance B! so as tooscillate at a frequency of 880 c. p. s.,

the signal of 1760 c. p. s. impressed upon the.

- plate circuit of oscillator l2 by condenser C9, and

. a similar condenser Clo is provided for coupling the oscillator l2tothe oscillator generating a frequency an octave lower than that ofoscillator l2.

It will be noted that the stabilizing signal from the higher frequencyoscillator, as for example, the signal from the master oscillator to, isimpressed upon the oscillator H across the plate winding of thetransformer T2 of the oscillator ll. Thus, the voltage of thisstabilizing signal is stepped up by the transformer T2 and impressedupon the grid of the tube 30. By virtue of the fact that the voltage ofthe stabilizing signal is effectively increased due to the step-up ratioof the transformer, it is possible to use a coupling condenser C3 ofrelatively low value. It is, of course, desirable .that the couplingcondensers C3, C3, CID, etc. be of low value to minimize the possibility'of a signal of appreciable amplitude being derived from a lowerfrequency oscillator when the signal output circuit of a higherfrequency oscillator is completed.

The useful signals from the master oscillator I0 and the controlledoscillators H and I2 are derived from their respective potentiometerresisters R3 and B8, through conductors 3|, 32, and 33 respectively.

In the instrument herein described, it will be assumed that when theconductor 28 is connected to ground, the master oscillator 10 will betuned to the frequency of the note All of the highest octave, whereaswhen the grid of the oscillator ill is connected to ground through boththe ad- 'justable resistors R4 and R5, the oscillator Ill will be tunedto the note A of the highest octave. The controlled oscillators ll, l2,etc. will of course change in frequencies from the notes Ali to A oftheir respective octaves as the frequency of the master oscillator 10 ischanged from the frequency of the note A5t to that of A5.

In Fig. 1, keys A3, A319, All, A4i, A5, and A5# are diagrammaticallyillustrated as representative of the complete keyboard of theinstrument. Each of the keys A5, A4 and A3, upon depression, closes twoswitches 34, 35, connecting their respective conductors 3!, 32, and 33to a bus 36, which is adjustably connected to a coupling resistance 38,one terminal of which is grounded and the other terminal of which isconnected to an amplifier 40 which supplies'a speaker 42. Atsubstantially the same time, the depression of the keys A5 and A4, and,A3, by the closure of their switches 35, respectively connectconductors 3! and 32 to a bus bar 44, which is likewise connected to anadjustable tap on the coupling resistor 38. The closure of theseswitches 34, 35 thus results in the transmimion to the amplifier of asignal derived from one or more of the oscillators "I, ll, l2, etc. Therelative amplitudes of the signals derived from the two oscillators upondepression of a single key are controlled by the adjustment of theconnection 2: the bus bars 36 and 44 to the coupling resistor Thedepression of a single key may therefore result in the simultaneoustransmission to the output ciruit of signals from two of the oscillatorsIII, N, l2, etc., in desired relative amplitude relations, thusproducing the eifect of organ couplers. If the signal from one of thetwo oscillators is not desired, one of the buses 36 or 44 may beconnected to the grounded end of the coupling resistance 38.

It will be noted that each of the keys An, Ad,

and A53 is adapted to operate not only its switches 34 and 35,corresponding to those for, the keys A3, A4, and A5 respectively, butalso operates a switch 46, closure of which connects the conductor 28 toa grounded bus bar 48, thus shortcircuiting the adjustable resistance R5and tuning the master oscillator ID to the frequency of the note ASt,consequently tuning the oscillators ll, I2, etc., to the notes All oftheir respective octaves. The switches 46 are arranged to close beforethe switches 34 and 35 close, upon the depression of a key, so that theoscillators will have been shifted to their At frequencies before theswitches 34, 35 close and the transmission to the output of undesirabletransients incident to the changing of the frequencies of oscillation ofthe oscillator is thereby avoided.

InFlgs. 2 and 3 is shown a modified key switching system whereby theresults of the switching arrangement shown in Fig. 1 may be obtained,using fewer switches. -As shown, the key A3 is adapted to depress anactuator 50 of insulating material, which operates switch contact armsII and 52 to complete circuits with bus bars 3i and M respectively.Beneath the key A33 is an actuator 5| which, upon depression of the key,causes completion of a circuit between a switch arm ii and grounded busbar 48. The actuator 5| is so arranged that it will be operated upondepression of either the key A3 of the key A32, while the actuator 54 isoperated only upon depression of key A.

The spacing between the upper ends of the actuators 54 and the keys issuch that when the key A33 is depressed, the actuator 54 will be engagedfirst so as to complete the tuning circuit for theoscillator (byconnecting the switch 56 to the bus ll) before the key operates theactuator 5| to complete the circuits between the switch 5! and bus 38,and switch arm 52 and bus 44. Thus, upon the depression of the key Alt,

the oscillators II, I I, and I! will be tuned to their A! frequenciesbefore the signals derived from these oscillators are transmitted to theoutput circult.

In playing the instrument, it seldom happens that adjacent notes, suchas Al and AI! will be simultaneously depressed. However, even if theyare depressed simultaneously, it will be noted that the only undesiredresult will be that the note A4 will not be sounded. In a completeinstrument, the octave interval notes, 1. e., all of the notes havingthe same musical scale designations, for example, all the A notes willhave their frequency supplied by one series of frequency stabilizedgenerators, such as is represented by the oscillators II, H, and II.This series of oscillators will also, as previously described, furnishthe frequencies for the At octave interval notes, i. e., all of the Atnotes within the gamut of the instruments In a similar manner, a groupof frequency-interlocked generators will be provided for all the octaveinterval notes B and the octave interval notes 0. similarly, anotherseries of frequency-interlocked generators will be provided for all ofthe Ct and D notes, for all the Di and E notes, for all the F and F!notes, and for all the G and G! notes.

Since, upon completion of the signal circuit by which the signalimpulses from the oscillators are transmitted to the amplifier andspeaker, the

mcillators are tuned to the desired frequency because of the priorcompletion of the tuning circuits, the undesired transient frequenciesincident to tuning the oscillators through the semitone interval are nottransmitted to the amplifier and speaker. By utilizing the key switcharrangement shown in Figs. 2 and 3, it will be apparent that a largenumber of key switch contacts may be eliminated. Although in Fig. 1 thecircuit is illustrated in a simplified form wherein the depression of akey results not only in sounding the note corresponding to the key, butalso sounds the note an octave higher, the coupler system may beextended so that other harmonic frequencies may be simultaneouslytransmitted in controlled amplitudes to the amplifier and speaker.

Furthermore, it will be understood that while I have shown and describedpreferred embodiments of my invention, it will be apparent to thoseskilled in the art that numerous variations and modifications may bemade without departing from the basic principles of the invention. Itherefore desire, by the following claims, to in- .clude within thescope ofmy invention all such equivalent or similar constructionswhereby substantially the same results may be obtained by substantiallythe same or equivalent means.

I claim: I

1. In an electrical musical instrument having an output circuit, incombination, a master generator, a second generator having a fundamentalfrequency different from said master generator but locked thereto in asimple fractional ratio, a keyboard including a first key and a secondkey, two electrical circuits completed by operation of said first key,one.of said circuits being connected to said master generator and beingeffective to alter the frequency thereof, the other of said cir cuitsconnecting said second generator to the output circuit of the instrumentto produce a given note, and means operated bysaid second key connectingsaid second generator to the output clr cult of the instrument toproduce a note of frequency difl'ering from that of the note produced byoperation of said first key.

2. The combination set forth in claim 1, in which said master generatoris an electron discharge device oscillator of relatively high frequencyand in which said second generator is an electron discharge deviceproducing a frequency which is one octave lower than that provided bysaid master generator.

THOMAS J. GIDRGE.

